Conventionally, in the machining tools including a machining center and a lathe, a linear guide rail is disposed on a base for slidably guiding a given member in the longitudinal direction.
The linear guide rail is positioned relative to the base by abutting one side of the linear guide rail on a reference face consisting of a vertical step formed on the base along the longitudinal direction and fastening a fixing bolt.
However, in such a linear guide rail, the inner diameter of an insertion hole for receiving the fixing bolt is defined larger than the outer diameter of the fixing bolt and thus a clearance is created between the fixing bolt and the insertion hole, resulting in the failure of accurate contact between the one side of the linear guide rail and the reference face.
Accordingly, a pressure holding device serving as a fitting member positioning device is abutted on the other side of the linear guide rail to press the linear guide rail toward the reference face.
FIG. 1 is a cross-sectional view illustrating a fitted state of a conventional pressure holding device, and FIG. 2 is a plan view of a conventional pressure contact member.
In these figures, reference numeral 11 denotes a base serving as an installation portion, 12 denotes an insertion hole formed in a predetermined position of the base 11, and 20 denotes a pressure holding device fitted in the base and functioning as a fitting member. The pressure holding device 20 includes a pressure contact member 13 and a fixing screw 14 for fixing the pressure contact member 13 to the base 11.
The pressure contact member 13 includes a cylindrical boss 15 received in the insertion hole 12 and an eccentric cam 16 formed adjacent to the boss 15 and abutted on the side of an unillustrated linear guide rail on the base 11.
The eccentric cam 16 includes a rectangular portion 18 for gripping the pressure contact member 13 by a spanner or the like for rotation, and a semi-circular pressure portion 19 for pressing the side of the linear guide rail along with rotation of the pressure contact member 13. In addition, the shaft center of the pressure portion 19 is offset from a shaft center Cn1 of the boss 15, and as the pressure contact member 13 is rotated, a distance m1 between an outer circumferential surface S1 of the pressure portion 19 and the shaft center Cn1 of the boss 15 changes depending on a rotation angle of the pressure contact member 13.
The base 11 has a screw hole 22 formed therein in communication with the insertion hole 12, while the pressure contact member 13 has a through hole 23 formed therein for the fixing screw 14 to pass therethrough in a concentric manner with the screw hole 22. In addition, the through hole 23 has a hole 25 formed in the boss 15 and having a circular section, and a screw seat 26 formed in the eccentric cam 16 in communication with the hole 25 and having a conical section.
Moreover, the fixing screw 14 consists of a countersunk head screw, including a thread portion 27 and a head portion 28 formed adjacent to and integrally with the thread portion 27 and having a conical shape. By passing the thread portion 27 of the fixing screw 14 through the through hole 23 to be threaded in the screw hole 22, the head portion 28 is pressed against the screw seat 26.
For the pressure holding device 20 with the above-described configuration, by loosely threading the thread portion 27 and the screw hole 22 together and rotating the pressure contact member 13 by a spanner or the like while the fixing bolt of the linear guide rail is loosened and the reference face abuts on the one side of the linear guide rail, the outer circumferential surface S1 of the pressure potion 19 presses against the other side of the linear guide rail depending on a rotation angle to push the linear guide rail toward the reference face and thus the one side of the linear guide rail and the reference face abut each other.
Consequently, by fastening the fixing screw 14 while the one side of the linear guide rail and the reference face abut each other and fastening the fixing bolt, the pressure contact member 13 is fixed in a predetermined position relative to the base 11. Thus, the linear guide rail can be positioned relative to the base 11 while the one side of the linear guide rail and the reference face accurately abut each other (for example, see Patent Document 1).    Patent Document 1: Japanese Patent Application Publication No. 2003-311631